Engineering

Electronics

Oscillation induced dies away over time if it is not kept going by a source
Resistance is unavoidable (real circuits)

Programming

Code re-factoring
- Determine when a replicated piece of code replaced by a procedure
— copy and paste the code once
— replicated three times, extract into a new procedure.
Duplication is considered harmful and a bad practice (code harder to maintain).
Code changes - change it in all places correctly, error-prone
Code in only one, easily changed.

C++ programming

Class method definitionsLaw of The Big ThreeThe Big Three
- If a class defines one of three functions, it should probably explicitly define all three:

destructor

copy constructor

copy assignment operator

All are special member functions.

If not declared, implicitly implemented by compiler with default semantics on all members of class

Destructor - Destruct object's members

Copy constructor - Construct object's members from equivalent members in copy constructor's parameter

Assignment operator - Assign object's members from equivalent members in assignment operator's parameter

Content

Many things are structured in threes

"Omne trium perfectum" : Latin phrase
- "everything that comes in threes is perfect", or
- "every set of three is complete"

Writing

Writing principle
Things that come in threes are inherently "better" than other numbers of things

Reader/audience likely to consume information written in groups of threes
- Eamples
— "Go, fight, win!" (slogan)
— The Three Stooges
— The Three Musketeers
— Three Little Pigs
— Three Billy Goats Gruff
— Goldilocks and the Three Bears
— Three Blind Mice

Series of three progression
- tension created
- tension built up
- tension released

Moon, the Earth and the Sun
- Positions, masses and velocities data set (directly or indirectly) of three bodies in time
- Determine the motions of the three bodies
- Find positions at times with laws of classical mechanics (Newton's laws of motion and of universal gravitation)

Motion of three particles models
- particles are considered as point masses, neglecting shape and internal structure
- interaction is a scalar potential (gravity or electromagnetism)

Mathematics

Economics

Business and EconomicsCompetitors in market
Explains mature competitive markets three 'major players'
- Will be three major competitors in free markets within any one industry
Industries with exactly three generalists outperformed every other industry structure
Other than the three major competitors, businesses only succeed if able to operate in a niche market

Medicine

Calculated confidence limit (no events observed)
If no major adverse events in a group of n people, 95% confidence that chance of major adverse events is less than one in n / 3 (or equivalently, less than 3 in n)
- approximate result, good when n > 30